Magnetic tape drives which utilize large reels of magnetic tape (e.g., 0.5 inch wide tape having a length of 2400 or 3600 feet) typically include DC motors for powering the supply reel and the take-up reel. Such DC motors require a voltage which is porportional to the linear velocity of the magnetic tape in addition to the voltage required to drive current through the armature of the motor. As a result, for a fixed rewind tape velocity, the DC motors require a changing voltage as the tape rewinds from the end of the tape to the beginning of the tape. The change of voltage during rewinding of a 0.5 inch tape drive is roughly 2:1 since this is the total radius change.
Thus, in conventional tape drive systems, the voltage to each of the reel motors changes as tape is wound from one reel to the other (e.g., during rewinding operation) when the tape velocity remains fixed.
The rewind time for a magnetic tape which is 2400 feet long is two minutes in conventional tape drive apparatus. The rewind time for a magnetic tape which is 3600 feet long is three minutes in such apparatus.